20180913

Astronomy quiz question: Jupiter's retrograde motion

Astronomy 210 Quiz 2, fall semester 2018
Cuesta College, San Luis Obispo, CA

The locations of Earth, Mars, and Jupiter are shown in the diagram below (not to scale, and orbits have been simplified as circles instead of ellipses).


Jupiter is __________ retrograde motion.
(A) about to start.
(B) in the middle of.
(C) just completing.

Correct answer (highlight to unhide): (C)


Retrograde motion occurs for Jupiter when the sun, Earth, and Jupiter are aligned (Mars in opposition). Drawing in lines from the sun to Earth and the sun to Jupiter indicates that Earth (which travels faster along its inner orbit), has already overtaken Jupiter (which travels slower along its outer orbit), thus Jupiter has already completed its retrograde motion.

Section 70158
Exam code: quiz02Sl3I
(A) : 18 students
(B) : 7 students
(C) : 11 students

Success level: 32% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.40

Section 70160
Exam code: quiz02N3r1
(A) : 6 students
(B) : 7 students
(C) : 3 students

Success level: 20% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.25


(Animation from marsprogram.jpl.nasa.gov)

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